It is well known by persons familiar with the free piston engine that it is comprised of pairs of cylinders with each pair coaxially aligned and disposed back to back with the piston rods extending from the pistons reciprocating in each of these cylinders also coaxially aligned and being joined by a yoke. Perhaps the most well-known free piston engine arrangement is the so-called Bourke engine, named after Russel Bourke. In a free piston engine the center of the yoke is transversely slotted to receive the throw of a crank so that, as each pair of pistons and their yoke-joined piston rods reciprocate as a unit, the crank throw will not only be reciprocated with and in the direction of the yoke, but it will also reciprocate transversely in the yoke slot. Thereby, there is imparted to the crank shaft the desired rotary driving motion from the reciprocation of the paired pistons which are interconnected through their rods and the yoke to move reciprocally as a unit. Bourke engines have been the subject of U.S. Pat. Nos. 2,122,676, 2,122,677 and 2,172,670 and the history and details of which engines are more fully described in a publication entitled “Bourke Engine Documentary” by Lois Bourke, wife of inventor Russel Bourke, copyrighted by the author in 1968, and printed by D. D. Enterprises of North Hollywood, Calif. 91601.
As for the lubrication system design of the Bourke engine, the crankcase includes a lubrication sump system where the crankcase is filled with oil as normally seen in conventional four stroke engines and is separated from the cylinder heads, which consequently operate as more of conventional two stoke engine. The oil within the crankcase is used to lubricate the main crankshaft bearings, the yolk bearings and the piston connecting rods and their respective bearings by means of a simple rotating splash method. In addition, oil from the crankcase is transferred via a small conduit to the cylinders and is strategically positioned to drip oil on the piston rings as they reach bottom dead center. As seen by evidence in actual Bourke engines built over the years, and as seen on the actual Bourke engine which was recently discovered, the oil from the crankcase migrates into the combustion chamber by leakage at the connecting rod bearing seals. Furthermore the oiling method used for the described piston rings allows excess oil to also drip into the combustion chamber. This passage of oil from the crankcase into the combustion chamber results in an excessive buildup of burned oil seen as a varnish buildup within the bottom end of the cylinders and the actual combustion side of the cylinder heads.
In the fuel and air induction system of Bourke engines, it is important to make note of the fact that the Bourke engine would not run on conventional pump gas. It would only run on a blend of two parts heavy fuel mixed to one part of white gas which further contributed to its resistance for becoming a main stream power plant of choice. The Bourke engine uses an intake manifold that is secluded from the oil filled crankcase. Air enters a carburetor that is attached to the intake manifold, it is mixed with fuel and then travels down the intake manifold to be pulled into the underside of the piston cavity which creates a vacuum as the piston travels upward on the compression stroke. As the piston moves downward on the power stroke the piston skirt closes the intake ports and compresses the induction charge underneath the piston. This compressed induction charge is not displaced within the crankcase as seen with all conventional two stroke engines. Prior to reaching the bottom of the piston travel a set of intake transfer ports allow the fuel mixture to enter the cylinder, fill the cylinder with a fresh fuel air charge, and scavenge the burnt exhaust gasses by means of allowing the exhaust to exit via the exhaust port.
While the theory and principle of operation of the Bourke engine are such that this engine offers many advantages over some more conventional internal combustion engines, certain mechanical problems along with a custom non pump gas specific fuel mixture have been observed in Bourke type engines which have heretofore been built and tested, and these problems appear to have contributed to the apathy of engine builders toward the Bourke engine.
For one, given the fact that a substantial amount of fuel air pressure is present underneath the piston as it reaches bottom dead center, the sealing methods available at the time and even under current times, allow leakage of the said fuel air charge to migrate into the oil filled crankcase area which results in an undesirable pressure increase within the oil filled crankcase. In addition the vacuum that is created as the piston travels upward on the compression stoke causes oil to be pulled into the lower section of the cylinder and therefore contaminating the fuel air charge with oil from within the crankcase.
Furthermore, the Bourke engine design was also based on a combustion cycle principal that to this day has never been validated and according to experts in the field is not plausible. Claims were made that the carbon fuels were compressed and ignited simultaneously during the compression stroke cycle causing both heat and pressure to release hydrogen molecules that would then greatly contribute to the power available from the fuel air charge being burned. As a result the Bourke engine combustion chamber and cylinder head did not utilize proper combustion chamber designs to maximize proper flame front propagation and fuel burn. It is the opinion of some that what is occurring is the early undocumented discovery of what is known today to be homogeneous charge compression ignition (HCCI). As a result the Bourke free piston engine needed to be run at a specific compression ratio for a given days atmospheric conditions with specific timing curves and a custom blended fuel in order to properly induce what was apparently the first undocumented HCCI engine operation. According to Russell Bourke, the Bourke engine cycle ran on a much leaner fuel air mixture than conventional IC engines, it would self-ignite under what he called the detonation cycle, and would run cold due to what he referred to as the refrigeration cycle of the burnt expanding gas as the piston traveled down on the power stroke and increased the volumetric cylinder area. It is the present understanding that HCCI requires a very specific compression pressure and temperature along with a leaner homogeneous fuel air charge which, when compression ignited, does not produce a flame front, and therefor contributes to lower exhaust gas temperatures common with what Bourke referred to as the refrigeration cycle.
Therefore, a need exists to overcome the problems with the prior art as discussed above.